HE PLURALISTIC OR BIOPYSCHOSOCIAL model of illness acknowledges that social factors play a role in the development of physical and emotional illness. Or, in Cassel’s language, that there is a “contribution of the social environment to host resistance.“’ Research continues to explore those social variables which directly or indirectly contribute to pathophysiologic processes, vulnerability to illness, symptom formation, and treatment response. One major area of research concerns the influence of stress and life events beginning with early writings of Cannon2 and Adolf Meyer.-’ Since the development of quantitative instruments for measuring life events, pioneered by Holmes and Rahe,4 there has been a flurry of studies examining the relationship between this variable and a variety of dependent symptom variables. Unfortunately, life events have rarely accounted for more than 15% and frequently less than 10% of the variance in any psychiatric outcome measures. Cognizant of the limits of a parsimonious theory linking stressful life events to illness, Caplan5 and others have suggested that social supports or social networks may be an intermediary variable serving to buffer the potentially negative effects of stress. Subsequently, a variety of investigators have shown an inverse association between specific aspects of social support and the development of depression in the general population6 and in recent widows;’ an inverse relationship between social support and symptom severity has also been shown in unipolar populations. R.9 Components of social support have also been examined in relationship to schizophrenia,‘O anxiety,” and psychosomatic disorders.r2 In most of these studies, social support has emerged as a better predictor of outcome than life events, causing speculation that there is a direct effect in addition to that of buffering stress. Although the use of specific questions on aspects of social support (eg, number of friends, relatives in the immediate geographic area, presence of a close contidante) are useful, it became clear by the mid-70’s that quantitative instruments were needed to reliably assess social support in research investigations and clinicians. This report presents the rationale, design, and psychometric testing of one instrument-the Social Support Network Inventory (SSNI)--which the authors began developing in 1979. It should be noted that other investigators such as Pattison” began developing similar instruments at that time; an excellent review of the methodology of these instruments has been provided by Lin.13